SPECTRAL METHODS FOR MODELING AND ESTIMATING VIBRATION FATIGUE DAMAGE IN ELECTRONIC INTERCONNECTS
SPECTRAL METHODS FOR MODELING AND ESTIMATING VIBRATION FATIGUE DAMAGE IN ELECTRONIC INTERCONNECTS
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Date
2023
Authors
Welch, Jacob Adam
Advisor
Dasgupta, Abhijit
Citation
Abstract
The purpose of this thesis is to explore the accuracy of fatigue damage estimation in printedwiring assembly (PWA) interconnects, using purely frequency-domain (also known as spectral)
information such as the power spectral density (PSD) of the input excitation. The test case used
in this study is the estimation of fatigue damage accumulation rate in the critical interconnects of
low profile quad flat-pack (LQFP) components on a PWA, under broad-band random vibration
excitation. this study examines whether the fatigue predictions made with this frequency-domain
approach are consistent with those obtained from a direct time-domain approach. The
frequency-domain response modeling is achieved using a two-stage global-local modeling
process using a finite element model (in ABAQUS©), where the dominant modal participation
factors for the dynamic response is obtained using a dynamic global simplified dynamic finite
element model consisting of shell elements to represent the entire PWA. The PSD of the input
excitation is applied as a boundary condition and the PSD of the PWA strain response is
recorded at the base of critical components. The corresponding PSD for the dynamic strain
response at critical interconnects is estimated with strain-transfer functions (STFs) for each
dominant mode, obtained from detailed 3D quasi-static nonlinear local models of the component,
adjacent PWB, and the interconnects. The global-local STF provides a relationship between the
level of equivalent strain in the critical interconnects and the flexural strain at the adjacent
surface of the PWB. The STF for each of the dominant vibration modes is obtained by imposing
the corresponding mode-shape predicted by the dynamic global model on the PWB, in the quasistatic
local model, using multi-point constraint equations. The PSD of the equivalent strain in
the critical interconnect is then estimated via linear modal superposition. A deterministic
estimate of the cyclic fatigue damage accumulation rate in the critical interconnect is then
conducted with the Basquin high cycle fatigue (HCF) model and linear damage superposition
approach, by using three different spectral approaches for representing the strain severity with
estimated probability density functions (PDFs). The three approaches include: (i) Raleigh
method; (ii) Dirlik method and (iii) Range distribution function created with the Rainflow cycle
counting method. Methods (ii) and (iii) are derived from a pseudo time-history created with an
inverse Fourier transform. These frequency-domain results are compared to corresponding
fatigue damage estimates from a multi-modal time-domain analysis method, to assess the
consistency of the two approaches.